Gas turbine engines operate to produce mechanical work or thrust. Land-based gas turbine engines typically have a generator coupled thereto for the purposes to generating electricity. These generators apply a load to the engine. Land-based gas turbine engines have different modes of operation depending on the load applied to the engine. From an emissions and fuel consumption standpoint, land-based gas turbines are designed to operate most efficiently at a full power condition, also known as baseload, as that operating point is most common amongst users of land-based gas turbines. For example, a combustion system in a turbine operating at baseload would operate in a premix condition, where all fuel and air are mixed prior to ignition, thereby leading to a more complete burning of all fuel particles and lower emissions. However, when the power demand is lower, the load required by the generator on the engine is less, and therefore the engine is designed to operate at a lower power setting, so as to reduce fuel consumption. As such, typically the combustion process is different at lower settings (not optimal) and as a result, emissions are higher.
For instances in which the load on the engine is lower and the engine is not operating at full power, it is desirable, from an emissions standpoint, to provide conditions to the engine such that it believes it should be operating in a more efficient mode (premix). One system known in the art for accomplishing this is an inlet bleed heat (IBH) system.
An IBH system draws air from the compressor discharge plenum and directs it through a piping system to the engine air inlet, where it is injected into the inlet to mix with external air drawn into the engine inlet. Through this process, the addition of compressed air, which is at an elevated temperature (upwards of 800 deg. F.), elevates the temperature of the air entering the compressor and the combustor such that the reaction temperature in the combustor is high enough to keep the engine operating in a premix condition at a lower power setting. Normally, engines cannot drop below 75% load and maintain the more efficient premix combustion operation. However, by the addition of inlet bleed heat, this lower limit for premix operation can be extended down to approximately 50% load, depending on the air permit for the operating site.
When power demand is high and the gas turbine engine and associated generator are operating at 100% load, it is often desirable to obtain more power from the engine, and more megawatts (MW) from the generator. A second system, separate from the inlet bleed heat system, common to land-based gas turbines is a power augmentation (PAG) system. The PAG system directs steam from a steam source through a piping system and injects the steam into the air in the compressor discharge plenum. In the plenum, steam and air mix prior to passing through the combustor. The steam increases the mass flow of the fluid entering the combustor, such that additional work can be gained from the hot combustion gases by the turbine. This results in additional MW produced by the generator. When electricity prices are high, this can lead to increased revenue for the engine/generator operator.
Each of these systems are used to obtain greater performance from the gas turbine and generator. However, separate piping systems and controls are used for each of these systems, even though one system injects steam into the compressor discharge plenum and the other system draws air out of the compressor discharge plenum, at different engine conditions.